It is generally accepted that a low level of fluorine in mains water (0.4 to 1 mg • L–1 depending on the climate of the country concerned) promotes the formation of tooth enamel and protects teeth from decay. On the other hand, too much fluorine will destroy this enamel and cause a range of endemic type disorders that are generally called “fluoroses”: malformed teeth, staining of the enamel, decalcification, tendon mineralisation, digestive and nervous disorders, etc. These problems can appear in individuals for widely variable quantities of the product. Water must be discharged or treated as soon as it contains more than 1 to 1.5 mg • L–1 of F–. Some natural waters contain more than 10 mg • L–1 of fluorine. This concentration has to be reduced to approximately 1 mg • L–1 (the acceptable concentration falling as the average annual temperature rises); the European standard has set 1.5 mg • L–1. Many studies have been carried out to address the issue however little success has been reported up to date. Layered double hydroxides (LDHs) which readily undergo anion exchange reactions have been used as a suitable candidate for defluorination. Also there is regeneration of the material after removal of fluoride ions without releasing flouride ions back in to the water cycle. F- elimination using a nanofiltration (NF) operation will solve problems for-large-scale pilot plants in the future.Many defluorination projects have significant effectiveness on the prevention of endemic fluorosis. The concentrations of water fluoride were below 1 mg/L. Advanced on-site methods, such as under sink reserve osmosis units, can remove fluoride but are too expensive for developing areas. Calcium carbonate as a cost effective sorbent for an onsite defluorination drinking water system. Batch and column experiments have been performed to characterize F- removal properties. The present review discusses various techniques of defluorination of water.
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